The present invention relates to a coating device for coating a traveling web, and more particularly to a device for building up coating material pressure upstream of the doctor blade for assuring uniform coating and elimination of air inclusions.
Such a coating device is known from U.S. Pat. No. 3,418,970, which includes an applicator having an inlet-side lip and an outlet-side lip. Between them, the lips define a passage slot for coating composition. The lips are formed on a compact structural part which is connected to the application chamber in which the coating composition is supplied. The outlet-side lip is intended to run "dry" during operation, which means that none of the coating compositions is intended to emerge except for that which adheres to the web to be coated. For this purpose, very precise slots between the lips for the web of material are necessary. The application chamber is therefore supported here by hydraulic supporting elements which act against the hydrodynamic pressure which is produced between the lips and the web of material. From the lips up to the coating blade there is then a relatively long path of travel of the web of material. The advantage of this device appears to be that no lateral seals are necessary in the region of the lips. However, this device does not appear capable of preventing inclusions of air in the coating applied to the web of material.